Numerous devices are known in the prior art for controlling the vertical and horizontal passage of an article through a predetermined fluid environment. Such devices can generally be classified within one of two broad classifications; submarine and diving wing constructions for use in liquid environments; and flexible parachute constructions and rigid airfoil constructions used in gaseous environments. The present invention, while usable in devices in both classifications, is intended for use primarily in the latter classification and particularly with inflatable glide parachute configurations using cellular construction and ram air principles.
Since prior to the advent of gliding parachutes, for many years, parachutes were constructed by sewing a plurality of panels together to define a hemispherical structure when inflated. Some of these domelike parachutes have incorporated slits, vents, or baffles for controlling the flow of air therethrough, both to facilitate deployment and to provide maneuverability. However, these parachutes are adapted primarily for nearly vertical descent, and generally do not permit a load to be guided over substantial horizontal distances to a target landing area.
Recently, gliding parachutes have been developed for sport jumping, fire fighting, and military applications which can be readily manipulated to carry a load over a substantial horizontal distance. A typical gliding parachute is preformed and constructed in such a manner that when inflated it will define an airfoil in cross section. When a load is suspended from this type of inflated parachute, the parachute will glide forwardly and its airfoil shape will provide the necessary lift. By controlling the peripheral edges of the gliding parachute, the parachute and the load can be guided in their path of descent to a distant target. Numerous patents have been issued for ram air type gliding parachutes. U.S. Pat. No. 4,771,970 to Sutton, U S. Pat. No. 4,729,530 to Jalbert, and U.S. Pat. No. 4,705,238 to Gargano disclose recent examples of such ram air type parachutes.
Much emphasis has been placed on the fabric and rigging configurations of previous gliding parachutes in an effort to approximate, as close as possible, a conventional airfoil shape. This results in maximum lift for a given parachute area which in turn provides maximum glide.
In a multi-cell gliding parachute, upper and lower fabric canopies are connected by laterally spaced fabric ribs. Suspension or support lines are connected at their upper ends to the parachute either directly or through flairs and coverage downwardly to a harness or other load supporting structure. A plurality of control lines are connected at or near the trailing end of the parachute toward each side to permit control of steering and braking. The fabric sections of the parachute are normally made of a high strength, lightweight fabric of suitable porosity.
One of the primary goals of inflatable multicell gliding parachutes using ram air type operation is to provide stability and maneuverability which are controllable both vertically and horizontally as the parachute travels through the atmosphere. It is desired to create a parachute which simultaneously minimizes bulk and weight and which is controllable through the vast array of maneuvers. However, while substantial steps have been taken toward this end in recent years, further improvement is necessary and desired.
A number of patents disclose various attempts to improve the stability, maneuverability, and control of ram air type parachutes. Pravaz, U.S. Pat. No. 4,191,349 discloses an airfoil type parachute having an air outlet passage 10 formed on the upper wall to regulate air flow and prevent instability by enhancing laminar flow around the parachute. Additionally, this parachute is formed of two separate cells along the cord length (front to back), with an air inlet 20 opening into a passage disposed in front of the rear cell, and a passage 16 for air to exit from the passage. However, this second rear cell does not necessarily enhance performance of the parachute during vertical descent, stall recovery, or initial inflation of the parachute. Nor does the second cell and its air inlets and outlets enhance the operation of the first forward cell. Additionally, air inlet 20 is not closable.
U.S. Pat. Nos. 3,749,337 and 3,972,495 both to Jalbert are directed to airfoil type parachutes or airwings having a single cell along the cord length. These patents disclose, in FIG. 3 for example, forming in lower layer 16 an opening 26 covered by a grill 32. The opening is provided with a flutter valve in the form of a flexible layer of material 28. When the pressure under the lower layer 16 is greater than that inside the wing, the pressure moves the flutter valve away from opening 26 to fill the wing with air. The flutter valve closes opening 26 when the pressure inside is greater than the pressure outside. However, these patents teach that grill 32 such as a mesh is required to be placed over opening 26 to prevent the flutter valve from falling through the opening and impairing the aerodynamic performance of the airwing. Moreover, opening 26 on the bottom of the wing is used instead of a leading edge opening. Thus, rather than improving performance, as emphasized in FIG. 3 and explained in the text of the patent, this feature is required not to enhance wing operation but simply to permit it.
Sutton U.S. Pat. No. 3,822,844 discloses a ram air type parachute having an air outlets 24 formed on the top wall 18 of each cell. These air passageways are intended to maintain parachute buoyancy. However, air inlets 22 on bottom wall 20 are required, at least in part, to offset the loss of air through outlets 24. This is exacerbated by cross vent ports 25 which permit air to exit from one cell into another, and out of all of the cells through outlets 24, including the end cells, which can decrease performance of the parachute by reducing lift on the ends. Furthermore, air inlets 22 are not closable when the inside pressure is sufficient.
Thus, what is desired and not provided by any of the prior art patents, is a gliding ram air type parachute which has improved stall recovery, vertical descent, and initial inflation characteristics, all of which can be provided by a closable, pressure operated air vent opening formed on the lower skin of the parachute, and which supplements the leading edge air inlet. Toward these ends, an earlier embodiment of the present invention included a parachute formed of a plurality of parachute cells 10, as shown in FIG. 1, formed of an upper sheet 12, a lower sheet 14, and two side sheets or ribs 16. Each cell is divided into two compartments by a central sheet or rib 18. Lower sheet 14 is formed of a forward skin 20 and a rearward skin 22. Forward skin 20 forms the leading edge of lower sheet 14, rearward skin 22 forms the trailing edge, and forward skin 20 overlaps rearward skin 22. Forward skin 20 is attached at each end of its rear edge to a junction or hinge point of rearward skin 22 and a respective side rib 16. The central point of the rear edge of forward skin 20 is connected to the junction or hinge point of rearward skin 22 and central rib 18. A mesh panel 24 is formed across the air inlet 26 which is formable between the forward and rearward skins. During various maneuvers, when the air pressure outside cell 10 exceeds the air pressure inside, the rear portion or flap 28 of forward skin 20 billows upwardly to form an arc-shaped opening between respective side ribs 16 and central rib 18 to allow additional air to enter cell 10. When the air pressure inside cell 10 increases to exceed that outside, the interior air pressure forces flap 28 downwardly to close air inlet 26. However, because of the excess material on flap 28 required to form air inlet 26, flap 28 and the remainder of forward skin 20 does not lie flat when opening 26 is closed. Because this portion of lower sheet 14 is not smooth it creates drag. Additionally, mesh panel 24 is required to prevent flap 28 from billowing below and outside of cell 10 and creating drag. Mesh panel 24 adversely increases the weight and bulk of the parachute, thereby decreasing performance, and mesh panel 24 also increases the manufacturing requirements and costs by requiring additional material and sewing.